With the progress of the digital technology of electronic devices in recent years, nonvolatile semiconductor memory devices with a large capacity have been actively developed for storing data, such as music, images, and information. For example, nonvolatile semiconductor memory devices which use ferroelectrics as capacity elements have already been used in many fields. Furthermore, compared with the nonvolatile memory device using a ferroelectric capacitor, a variable resistance nonvolatile semiconductor memory device (hereinafter referred to as ReRAM) using a variable resistance element in which a resistance value changes according to the application of an electric pulse and the state is maintained draws attention in that it is easy to ensure consistency with a normal semiconductor manufacturing process.
Here, Patent Literature 1 discloses a variable resistance element which comprises a first electrode layer, a variable resistance layer, and a second electrode layer. Here, the variable resistance layer comprises by stacking two tantalum oxide layers having different oxygen content atomic percentages. In other words, the variable resistance layer comprises a stacked structure of the first tantalum oxide layer and the second tantalum oxide layer, and the second tantalum oxide material layer comprised in the second tantalum oxide layer is higher than the first tantalum oxide material layer comprised in the first tantalum oxide layer in oxygen content atomic percentage. It is disclosed that the second tantalum oxide layer having a high oxygen content atomic percentage is formed through performing an oxygen plasma process on the first tantalum oxide layer.
Moreover, Non Patent Literature 1 discloses a nonvolatile memory device which includes a variable resistance element using two transition metal oxide layers in which a transition metal oxide as a material is formed. As the transition metal oxide, four types of NiO, TiO, HfO2, and ZrO2 are disclosed.